Attempting to Extrude Imported SVG Curve
Your object is very very small and has a very large scale.


Select all your imported curves and apply scale with Ctrl + A > Scale
Join them all together with Ctrl + J (select them all and then make sure you click-select at least one last curve to make it the active object, so it will act as receiving curve other curves will be appended to)
Now enter edit mode in the new curve
Select all vertex and press Space Bar
Search for Set Curve Radius
Enter a value of 1.0and press enter


You should now be able to extrude successfully
You can now separate all curves again into their original parts by entering edit mode, selecting each spline individually and pressing P Separate

Just a side note, when using curves always prefer the builtin extrusion method over solidify, it is more reliable and has better features like allowing non destructive beveling